Carrier current communication system



Jan. 12, 1943. w. r. DENToN Erm.

CARRIER CURRENT COMMUNICATION SYSTEM 2 Sheets-Sheet l Fi-led Jan. 16, 1940 Jan.' l2, 1943. w. T. BENTON Erm..

CARRIER CURRENT COMMUNICATION SYSTEM 2 sheets-sheet 2 Filed Jan. 16. 1940 f ..1 WY w N.

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f vm P 9m.. vll/8 A oRNEv Patented Jan. 12, 1943 UNITED STATES PATENT OFFICE CARRIER CURRENT CQMMUNICATION SYSTEME William T. Denton and Herbert D. Goetze, Los Angeles, and Edwin W. Morris, Santa Monica, Calif., assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a. corporation of Pennsylvania I Anolicetion January 1s,"i94o, serial No. 314,070 2 claims. (ci. '1n-353) This invention relates to carrier current comthese signals to reestablish the operation of the munication systems and, more particularly, to receivers at their full sensitivity.

systems of carrier current supervisory control Another feature of this invention is that the distributed over power line circuits. control operation is independent from the transf Supervisory control signals transmitted over v mission level ofthe signal frequency being based- :power transmission lines make use of a carrier upon the fact that the interference includes channel. Such a channel consists of semi-high a wide band of frequencies whereby the control frequency transmitters and receivers connected may be effected by any frequency Which iS Outto the line through suitable coupling capacitors Side f the Signal Channel. The response to and tuning units. The supervisory control sigfrequencies other than the transmitted signal nais are converted into coded carrier frequency and the conversion thereof into a desensitizins impulses. factor is the function of the interference elim- Iti the operation of a system of the above type, inator in accordance with the present invention. it is extremely important that none other than A further advantage 0f the System herein detheftransmitted impulses shall actuate the control l5 scribed is the simple circuit arrangement which equipment which, in turn, operates the various may easily be applied t0 Various types 0f Carrier ch; uit breakers and switches. Faulty operation current as Well as radio broadcast receivers, the due to signals originating from disturbances OperatiOn theleOf beine entirely automatic.

having frequency components within the signal Other featilleS and advantages Will be apfrequency may cause serious damage and is Often parent from the following description of the in' also a hazard to the safety of human lives. The ventien, pOinted Out in partieularity bythe apdisturbing signals may originate in the opera- Dended claims and taken in connection with tion of disconnects and oil circuit breakers, atthe aCCOInparlying drawings, in which: mospheric and lightning disturbances which Figure 1 is a schematic circuit shell/insr in propagate transients having steep wave iront block diagrams a carrier current distribution characteristics. Since these transient disturb- System fOl Supervisory Control utilizing the inanoeo cover a wide range of frequencies, they terference elmination in accordance with this include frequency components of the signal freinvention; and

quency channel to which the equipment is tuned, Fig- 2 iS a Schematic Circuit diagram of the and create extraneous impulses which, being interference eliminator applied to a standard within the admittance bend of the receivers, will type cf carrier current receiver.

cause operation of the receiver relay In Fig. 1, the carrier communication system Lowering the sensitivity of the receivers to a 'is Shown t0 include two stations, both having degree of no response to Such extraneous siga transmitter and a receiver, the latter actuatnals, as was customary in prior arrangements, ing the operation of the supervisory control has the disadvantage that the receiver will not equipment- This ligure ShOWS a Simple installaoperate on desired signals of smal] magnituda tion, although depending upon the length of the Carrier frequency transmission over line con- Power distribution netWOIky a number 0f other ductors may vary within wide limits depending transmitter and receiver stations may be used. upon various factors of power line conditions. 4o FOI Simplifying the illUStratiOn, Only a Straight Therefore, it is necessary for successful relaying portion of the power line is shown comprising that the receivers maintain high sensitivity in Conductors l. 2 and 3 which may be any direct order to respond to low levels of signal impulses 01' alternating Current System- SWtCheS 4 and also. 4 are shown as an example of the type of equip- 'rhe particular feature of this invention is that 45 ment which 1S Operated by the supervisory c011- the operation of carrier frequency receiving systml equipment v tems as to the desired signals is maintained with It is not believed necessary to show in detail high receiver sensitivity at all times whereas the Various C11' Cults 0f the DOWeI distribution Systhe operation of the receivers is automatically tem: Particularly the dill'elent type 0f switching suspended during the presence of interfering Operations Which the Supervisory control equipsignals having frequency components within the ment S Called 1113011 t0 perform. The invention admittance band ofy the reoeivers To this end, resides in the carrier current communication feameans are provided for automatically disabling ture Which is established between points A and the receivers in the presence and for the dura- B IOCaled 810118 the DUWeI llne- At the pOiIltS betion of interfering signals and upon cessation of tween stations A and B, the transmitter and ,the

primary indexes.

receiver are suitably coupled to the line by meansv of coupling transformer 5, the primary 6 of which connects through the loading inductance 1 and coupling capacitor 8 to line 3. The other terminal ofthe secondary winding is grounded and in this manner the circuit is completed between re-y to sendsignal impulses and operate at a frequency band which may be called a semi-high frequency in the neighborhood of 60 kllocycles. The

capacitor i6. Bypass condenser il is connected to the grid return circuit which continues through resistor i8 to a source of bias potential over conductor i9. The primary 2D of the transformer i5 is connected to the secondary winding 2i of the line'coupling transformer 5. For maximum cur. rent transfer in the circuit, the secondary winding 2i has various taps and a tuning condenser 23 is serially interposed. A neon glow light 2t in shunt with the winding it acts as a limiter load for large voltage surges. The screen grid 25 of tube ii is suitably by-passed by condenser carrier frequency impulses sent out by the transmitter in a certain prearranged code are to be intercepted by receivers located at distant points, such as the one at station B, and vice versa, impulses sent by the transmitter located at other stations are to be received at station A by the receiver.

Rponse of the receiver tothe carrier fre- Y quency signal results in actuation of the relay connected thereto which operates suitable circuits in the supervisory control equipment. Despite the insertion of filter networks shown schematically by the parallel tuned circuits Q and ill.

transient impulses originating from various sources in a power line systemvare disturbing in that when received bythe receiver unwanted operation of the relay will result which causes actuation of the supervisory control equipment.

As stated before, these impulses have steep wave fronts and wide band frequency characteristics having frequency components within the admittance band of the receiver. Consequently tuned circuits, no matter how sharply resonant they may be, are inadequate alone. In order to eliminate the response to all frequencies including even the signal frequency when disturbances 26 and lter resistor 2i and connects to a positive potential source through conductors 28 and 29. The source of operating potential herein shown by way oi illustration is a conventional rectifledvand filtered alternating current power supply having a voltage divider in the form of resistors 3B, 3i, 32' and potentiometer 32. Filter condensers 33 and 84 and lter choke 35 are arranged in a conventional manner. Only part of the power supply circuit is shown, since all types of supplies may be used as long as the voltage and current characteristics thereof is suitable for the particular tubes in the circuit.

Continuing the description of the receiver, a local oscillator of the vacuum tube type is shown to supply lush-frequency voltage to the mixer grid 3@ of tube il. The various components of the oswhich can supply the required frequency in order to obtain the intermediate frequency to which the output circuit of tube ii is tuned. The latter occur, it is necessary to control the eective operation of the receiver.l This control is accomplished by means of a receiver control connected to the input circuit ofthe receiver to be energized by the extraneous impulses, the output of which is fed to a portion of the receiver in such manner as to produce ya certain controlling eect upon .circuit components. The receiver control is shown in block diagram as a separate unit in order to facilitate the understanding ofits operation. It is to be understood, of course, that the receiver control may also be built into the receiver as an integral part thereof without departing from the essence of this invention. 'Ihe equipment at station B is identical inevery respect with that of circuit, connected to the anode 3? of tube ivi, includes the tuned primary winding 38 or an intermediate frequency transformer 3l, the tuned secondary winding 3g' thereof being connected to the input circuit of an amplifier tube 39 between grid lil and cathode Iii.

The grid return circuit is bypassed by condenser llvlter resistance i8 and terminates at conductor 29, leading to the source of bias voltage which will be explained later. The output circuit connected to the anode 63 of tube 39 includes an intermediate frequency bypass capacitor it and choke coil d5, together with the energizing winding d6 of the relay dl'. The contacts it and 5S of the relay il may be connected for the closure or opening of any desired circuit, such for example,

as shown in Fig. l, indicated as a supervisory station A and the coupling components are indicated by the same reference characters having The coupling of the various units to the line is shown by a single transformer in this gure merely to simplify the illustration. Each-unit, such as the transmitter and the re'- ceiver, or the receiver control, may have seperate coupling impedances of the type most suitable for its input circuit with the same result as can be obtained by the coupling shown herein.

control equipment. Anode potentials for both tubes il and 39 and also for the oscillator tube 56 are taken Afrom the high potential side of the pwer supply through conductors 5i, 52, 53 and 5 The receiver circuit herein described is a simple superheterodyne generally employed for carrier current communication. Other types of receivers, for instance. tuned radio frequency circuits, of a suitable number of stages may be used. As long as the vacuum tubes utilized therein have such' high frequency impulses from the power line in the way as the signal receiver. The secondary winding 58 of transformer 5l is parallel tuned with capacitor 59 and connects between grid 60 and cathode 6| of'ampliiler tube 62. The grid return circuit is bypassed by the capacitor 53 and returns through filter resistor Si over conductor 65 to the center tap of the potentiometer 32 of the voltage divider circuit. The screen grid 66 of the amplifier tube S2 is connected through resistor 68 and conductor 29 in the usual manner to the screen potential tap of the voltage divider. 'Ihe screen is also bypassed by capacitor 61. The anode of this tube is connected to the positive supply throughs. parallel resonant circuit consisting of the primary winding B9 of radio frequency transformer 10, the tuning being effected by condenser li. The secondary l2 of this transformer is also tuned by means of condenser '13.

The voltage appearing in the secondary circuit is rectified by rectifier tube 14 which is in the form of a simple diode, the anode l therefor being connected to one terminal of the secondary winding 12 and the cathode 1S to the other terminal through a load resistance comprising potentiometer 'Il which is bypassed by condenser 18. The slide of the potentiometer Il is connected to the conductor i 9 which terminates in the grid return circuits of the amplifier tubes in the signal receiver. The cathode 'I6 of the rectifier 14 is also connected to the junction point of voltage divider resistor 32'. The latter being at a potential more negative than ground supplies the necessary minimum bias through the load resistance Il and conductor I9 for the grids of the amplifier tubes in the signal receiver.

In the operation of the system, the signal receiver circuits are carefully tuned to the selected signal frequency which, by way of example, may be 60 kilocycles. The circuit of the receiver control, however, is carefully tuned to a different frequency, usually slightly below the signal frequency, for example, to 55 k. c. It should be far enough removed from the signal frequency that the normal signalling will have no effect and should be close enough to easily pass the broad line tuning equipment. Frequencies slightly lower than the signalling frequency' are usually used on the theory that the lower frequencies from remote disturbances will attenuate less and hence be more effective for this purpose. As long as there is only the carrier signal, the receiver control circuit receives practically no excitation due to its resonant characteristics and no signal is being amplified by the tube 62. Consequently, there is no signal to be rectified in the output circuit thereof. As long as the rectifier is inactive, there will be no voltage across the load resistor l1 and the bias for the control elements of the amplifier tubes in the signal receiver will be the normal required potential for maximum sensitivity of operation, this being derived from the voltage divider resistor 32. As soon as transient impulses of any nature appear in the input circuits of the receiver as well as the receiver control, having frequency components bcyond that of the signal frequency, by only a small amount, for example, 5 kilocycles, the control circuit will be energized and the particular component of the transient impulse frequencies amplified by the tube 62 and the resulting high frequency voltage rectified by the rectifier 14. The unidirectional component of this voltage appearing across the load resistance 'Il will be additivev to the minimum bias voltage and instantly provides a bias potential for the amplifier tubes in the signal receiver.

By suitable choice of circuit constants, a bias voltage proportional to the interference level can be obtained in this manner, having suillcient magnitude tocompletely block the operation of the amplifier tubes in the signal receiver and in this manner prevent the actuation of the relay 4l. The amount of bias required may also be adjusted by the load resistance potentiometer, whereas the sensitivity of the control circuit can be adjusted by the potentiometer 32 in the voltage divider circuit.

In practical operation, this circuit was found extremely flexible and capable of delivering sufncient bias for disabling the signal receiver at even low levels of interfering transients. The tubes utilized in the receiver control giving satisfactory results were the type 77 for the radio frequency amplifier and the type 6H6 for the rectiner. The following values of circuit constants were found to give satisfactory results under actual operating conditions, and should be taken merely as aguidance since they must necessarily be varied to meet various conditions characterizing such installations.

The inductance value of the high-frequency transformers was approximately 15 microhenries and the coupling capacitor 55 was 250 micro-microfarads. The tuning condenser of the secondary winding 5l was approximately 70 micro-microfarads. The screen and grid return bypass capacitors were each IAO microfarad. Ihe radio frequency transformer coupling the rectifier had approximately the same characteristics as the input coupling transformer. The load resistance potentiometer 11 with approximately 20,000 ohms provided a bias voltage sufiicientfor blocking tubes il and Il.

'We claim as our invention:

l. In a system of radio signalling primary receiving means responsive to a certain signal frequency, secondary receiving means responsive only to a particular other frequency adjacent to said signal frequency, a circuit interconnecting said receiving means including means for controlling the operation of said primary receiving means upon responsive energizatlon of said secondary receiving means.

2. In a carrier frequency control system distributed over power lines, a signal frequency source, supervisory control equipment, a receiving arrangement comprising dual receivers one of which being tunable to a signal frequency is operable upon response for initiating the actuation of said supervisory control equipment and the other of said receivers being tunable to a frequency different from, but contiguous with, the frequencyspectrum of said signal frequency. said latter receiver being operable upon energizetion to prevent the responsive action of said first receiver.

WILLIAM T. DENTON. HERBERT D. GOETZE. EDWIN W. MORRIS. 

